The overall objective of the proposed research is to understand the mechanisms of inheritance of mitochondrial DNA (mtDNA) using the budding yeast S. cerevisiae, as a model organism. The proposed studies will combine genetic, biochemical, molecular, and cell biological approaches to identify and characterize the various components that contribute to the faithful transmission of mtDNA during vegetative growth. To these ends, investigators propose three specific aims: 1) To complete the detailed biochemical characterization of mtDNA-protein complexes (nucleoids) which are the segregating units of mtDNA. The goal is to identify by crosslinking procedures the major proteins interacting with mtDNA and to determine how these proteins contribute to the organization and propagation of the mitochondrial genome. 2) To analyze the functions of novel proteins and pathways required for mtDNA transactions. For example, the investigators will expand on the findings that the mitochondrial:chaperone, Hsp60, and some mitochondrial proteins whose expression is under general amino acid control, which they have found to be associated with mtDNA, influence mtDNA inheritance. 3) To analyze cis- and trans-acting elements controlling mtDNA replication and transmission in petite and wild-type strains. These studies will focus on the role of putative origins of replication (ori elements) in the phenomenon of hypersuppressiveness, the role of ori elements in the replication and transmission of wild-type mtDNA and the characterization of an activity that initiates rolling replication from an ori element. How cells transmit their mtDNA is fundamental and applies to almost all eukaryotic cells. It is now clear that a number of inherited disorders involve aspects of the segregation of mutant and wild-type mtDNAs. The investigators have developed a tractable experimental system in which to investigate these important issues.